Liquid crystal display devices are used in various fields as displays for watches, calculators, personal computers, personal word processors and the like because they can be made thin and light and driven with a low voltage. In TN (Twisted Nematic)-mode liquid crystal display devices the most widely used, electrodes are formed on the upper and lower substrates, liquid crystal having a positive dielectric constant anisotropy is sandwiched between the two substrates with a twist of 90° and switched between on and off states by applying an electric field perpendicular to the substrates. This TN-mode liquid crystal panel has a narrow viewing angle, causing inversion of intensity levels.
Liquid crystal displays using VA (Vertical Alignment) liquid crystal have been developed, in which liquid crystal having a negative dielectric constant anisotropy crystal is sandwiched between the substrates and, when no electric field is applied by a perpendicularly oriented film, the liquid crystal molecules are vertically aligned, and, when an electric field is applied, the liquid crystal molecules are turned in a lateral direction. This VA-mode liquid crystal display device can obtain a wider viewing angle compared to the TN-mode liquid crystal display. However, even in the VA-mode liquid crystal display, when the liquid crystal molecules are inclined in one direction and the liquid crystal panel is observed from that direction, inversion of intensity levels inevitably occurs.
In order to overcome that drawback, for example, Japanese Unexamined Patent Publication No. 1999-242225 and Japanese Unexamined Patent Publication No. 2000-305086, etc., disclose a method in which regularly arranged projections are formed in a display region and the orientation of the liquid crystal is controlled by these projections.
Japanese Unexamined Patent Publication No. 2000-206541 discloses a method in which formation of projections is achieved on one of the substrates for maintaining a constant gap (cell thickness) between the upper and lower substrates holding liquid crystal in between and formation of a flattening film is performed on the same substrate. However, Japanese Unexamined Patent Publication No. 2000-206541 discloses neither use of at least two types of projections having different heights nor a method for manufacturing the same. According to the arrangement disclosed in the above publication, the projections are formed between the pixel electrode and the opposing electrode and the flattening film is formed beneath the pixel electrode.
Aiming at achieving a wider viewing angle than that of the TN-mode liquid crystal display device, the OCB (Optically self-Compensated Birefringence)-mode liquid crystal display device has been developed. In the OCB-mode liquid crystal display device, liquid crystal molecules are oriented in the same direction along the upper and lower substrates (splay condition). Then, the array of the liquid crystal molecules is bent (bend condition) around the center of the panel by applying a DC voltage. Thereafter, the liquid crystal molecules are driven. In this method, a projected portion is formed to readily invert from the splay condition to the bend condition (Japanese Unexamined Patent Publication No. 1998-20284).
In the ASM (Axially Symmetric aligned Microcell)-mode liquid crystal display device having liquid crystal molecules axisymmetrically oriented in the liquid crystal regions which are divided by a polymer wall, an arrangement is known in which pole-shaped projections are formed on a part of the polymer wall (Japanese Unexamined Patent Publication No. 2000-081623).
In a transmission type liquid crystal display device, light emitted from a backlight enters into the liquid crystal panel from the back. On the other hand, in a reflection type liquid crystal display device, image formation is achieved by reflecting external light with a reflecting film without using a backlight. In the reflection type liquid crystal display devices, an arrangement is known in which the pixel electrode serving as the reflecting film is obtained by forming a photosensitive film on the surface of the substrate, obtaining a large number of asperities on the surface of the film by photolithography, and depositing aluminum or like metals on the film. (Japanese Unexamined Patent Publication No. 1993-232465).
As described above, formation of projections on substrates has been applied to various kinds of liquid crystal display devices. Several kinds of projections having different heights can be formed for serving different purposes such as to control the orientation of the liquid crystal or maintain a constant cell thickness, etc. at several kinds of liquid crystal displays.
However, in the heretofore known methods, several kinds of projections having different heights have been formed out of different materials in separate production processes. Therefore, in these methods, the production efficiency is low and the precise adjustment of the positional relationship between the different kinds of projections is difficult. For example, in order to keep the cell thickness constant, if spherical resin spacers are dispersed on one of the substrates and then the two substrates are attached to each other, the spacers (spherical resin) maintaining the constant cell gap and the spacers (projection) controlling the orientation are produced in different processes using different materials. Japanese Unexamined Patent Publication No. 2000-305086 discloses a structure in which, by forming some projections on a light-blocking film, division of orientation and maintenance of the cell thickness can be performed based on the variation of the projection heights. However, in this arrangement, the light-blocking film is a part of the high projections. Therefore, this method does not achieve the production of several kinds of projections having different heights in a single process nor projections which are entirely made of the same material.